We present 3.6-24 μm Spitzer observations of an unbiased sample of
nine luminous, dusty galaxies selected at 1200 μm by MAMBO on the
IRAM 30 m telescope, a population akin to the well-known submillimeter
or SCUBA galaxies (hereafter SMGs). Owing to the coarse resolution of
submillimeter/millimeter cameras, SMGs have traditionally been difficult
to identify at other wavelengths. We compare our multiwavelength
catalogs to show that the overlap between 24 and 1200 μm must be
close to complete at these flux levels. We find that all (4/4) of the
most secure >=4 σ SMGs have >=4 σ counterparts at 1.4
GHz, while the fraction drops to 7/9 using all >=3 σ SMGs. We
show that combining mid-infrared (MIR) and marginal (>=3 σ)
radio detections provides plausible identifications in the remaining
cases, enabling us to identify the complete sample. Accretion onto an
obscured central engine is betrayed by the shape of the MIR continuum
emission for several sources, confirming Spitzer's potential to weed out
active galaxies. We demonstrate the power of an
S24μm/S8μm versus
S8μm/S4.5μm color-color plot as a diagnostic
for this purpose. However, we conclude that the majority (~75%) of SMGs
have rest-frame mid/far-IR spectral energy distributions commensurate
with obscured starbursts. Sensitive 24 μm observations are clearly a
useful route to identify and characterize reliable counterparts to
high-redshift far-IR-bright galaxies, complementing what is possible via
deep radio imaging.